The present invention relates to dental instruments, methods and materials used to register jaw positions and to measure or record a patient's bite. In particular, the invention relates to a system for applying and removing dental impression material on bite forks, bite trays or other dental devices.
In simulating the jaw position and the alignment of a patient's teeth, dentists usually mount dental casts or molds of the patient's teeth in a dental articulator (jaw simulator). To produce an accurate simulation, the dental casts must be positioned to a standard or predetermined reference plane taken on the patient's head when the casts are mounted in the articulator. When positioning the casts in a jaw simulator, one required step is to form impressions of the biting surface of the patient's teeth or ridges on tools known as bite forks and bite trays. Bite forks and bite trays are generally thin plate-like carriers in the shape of a row of teeth. Such bite forks and trays or other such devices, when considered collectively, will be, for convenience, referred to as dental trays herein. Impressions of the biting surfaces of the patient's teeth are made in a soft bite impression material which has been attached to the dental tray. The bite impression material then hardens.
In practice, the bite impression material is usually applied by hand directly onto the dental tray. Typically, an impression material such as sealing wax is melted onto the dental tray by placing the end of a rigid stick of wax into a flame, such as that provided by a bunsen burner. As the end of the stick starts to melt, the material is dripped onto a clean, warm and dry dental tray in the desired areas. Normally, three small mounds of wax are formed on the top and also the bottom sides of the dental tray in this manner. The tray is sometimes roughened or has holes in the areas where the bite impression material is to be deposited to cause the bite impression material to adhere tightly to the tray. The wax becomes hard at room temperature, but the wax will melt and flow or drip when heated to about 200.degree. F. At a temperature of about 120.degree.-140.degree. F., it is soft and can be placed in the patient's mouth and used for obtaining an impression of the teeth, after which the impression material will accurately harden at body temperature.
After the dental tray has been used for its intended purpose and the impressions are no longer needed, the bite impression material is usually removed so that the dental tray may be reused. Removing the impression material is a difficult operation because it cannot simply be scraped away. For dental trays which mount the impression material in grooves or holes on the tray, removing the material is even more difficult. To remove the material, it is necessary to reheat the dental tray to soften and melt the material to be able to scrape it away. Both the application and removal of the impression material are time-consuming operations, which are usually done by a dentist or a highly paid assistant. Also, the task is unpleasant and somewhat dangerous because the flame and the hot wax involved often catch fire, splatter hot material and produce toxic fumes. Moreover, fuel and other clean-up supplies are wasted in applying and removing the bite impression materials.
Alternate methods and devices have been developed to eliminate the dangers and waste associated with the application and removal of the bite impression materials from dental trays. For example, dental bite forks have been made of disposable plastic with the impression materials deposited on the forks during the manufacturing process. After use, the entire fork with the impression material on it is simply discarded. However, these disposable plastic bite forks are too flexible. Bite forks should be very rigid for accurate registration of the teeth positions and for alignment of the dental casts in an articulator. Additionally, utilizing disposable plastic bite forks is expensive, since the tray and the impression material are used only once. Zinc oxide eugenol paste, as well as many other dental impression materials are also often used on bite trays. Most of these materials are difficult to clean from the tray.
Another method used to avoid the high costs that accompany applying and removing bite impression materials is the use of paraffin wax. This method wraps warm thin sheets of such wax around both sides of the dental tray. Although such wax is relatively cheap, it is difficult to make accurate impressions and the wax does not always firmly adhere to the dental tray. In addition, remnants of wax often remain on the dental tray after cleaning, which may prevent adequate sterilization after use. Unless strong, toxic chemicals are used or the wax is burned off, which both produce toxic fumes, it is difficult to remove all traces of contaminated wax from the dental tray used for previous patients.